REACTION OF TA THIN-FILM WITH SINGLE-CRYSTALLINE (001) BETA-SIC

The reaction between a sputter-deposited Ta film (320 nm thick) and a single crystalline (001) beta-SiC substrate induced by vacuum annealin g at temperatures of 600-1200-degrees-C for 1 h (30 min at 1100-degree s-C) is investigated by 3 MeV He++ backscattering spectrometry, x-ray diffraction, secondary ion mass spectrometry, and transmission and sca nning electron microscopies. No significant reaction is observed at 80 0-degrees-C or at lower temperatures. At 900-degrees-C, the main produ ct phases are Ta2C and carbon-stabilized Ta5Si3. A minor amount of unr eacted Ta is also present. After annealing at 1000-degrees-C, all the tantalum has reacted; the reaction zone possesses a multilayered struc ture of beta-SiC/TaC/carbon-stabilized Ta5Si3/alpha-Ta5Si3/Ta2C. The d iffusion path at 1000-degrees-C is plotted on the isothermal section o f the Ta-Si-C phase diagram. At 1100-degrees-C, the reacted layer has an interface with the SiC substrate that is still quite flat but has a rough surface due to the formation of macroscopic voids within the re acted layer. The equilibrium products predicted by the phase diagram a re TaC and TaSi2. This final state is reached by annealing at 1200-deg rees-C for 1 h. At that point, the reacted layer has a laterally very uneven structure and morphology.